First-principles studies, using local density functional theory, were made of the properties of (100) surfaces which were clean, or H-covered. The calculations were based upon a variational solution of the Kohn-Sham equations, using a preconditioned conjugate-gradient approach, and upon an optimization of the atomic structure. It was found that the clean and monolayer-covered surfaces reconstructed in a (2 x 1) cell, via the formation of rows of symmetrical -bonded dimers. Further hydrogenation, to a coverage of 1.5 monolayers, stabilized a surface with a (1 x 1) periodicity of the C layers; although there was a low H-desorption energy for the formation of the reconstructed monohydride surface. The 2-step desorption process was in good agreement with experimental observations. Electronic surface states within the bulk gap were predicted for the clean surface, but not for the monohydride case. Detailed analysis of the layer-resolved local densities of states, and of the dispersion of the surface states, demonstrated that the results were in good agreement with recent photo-emission data. A negative electron affinity was predicted for the monohydride surface, but not for the clean surface.

J.Furthmüller, J.Hafner, G.Kresse: Physical Review B, 1996, 53[11], 7334-43